MOLYBDOVANADOPHOSPHORIC ACIDSAND THEIRSALTS 437
Vol. 7, No. 3, March 1968
agreement with other fluorosulfates, the S=O symmetric and asymmetric and S-F stretching frequencies occurred over a narrow 11,14,l 8 , I 9 Some other tentative assignments are also given. The FI9 nmr results are summarized in Table IV. All of the compounds showed an F19 resonance in the fluorosulfate region a t about 9 -50.20 The Flg reso(18) D. D. Des Marteau and G. H. Cady, I n o v g . Chem., 6, 169 (1966). (19) D. D. Des Marteau and G. H. Cady, i b i d . , 6, 1829 (1966). (20) F. A. Hohorst and J. M. Shreeve, ibid., 8 , 2069 (1966).
nance for the fluorosulfate group was shifted downfield as successive replacement of chlorine by fluorosulfate occurred. For the thionyl fluorosulfates the S-F resonance was slightly broadened. For SiClZ(OS0zF)z the high-resolution nmr showed a sharp resonance with a broad resonance slightly downfield. Acknowledgment.-The author gratefully acknowledges Professor G. H. Cady for helpful suggestions and generous use of his research facilities. The nmr spectra were taken by Mr. B. J. Mist.
CONTRIBU~ION FROM THE CLIMAX MOLYBDENUM COMPANY OF MICHIGAN, RESEARCH LABORATORY, ANNARBOR,MICHIGAN 48105
Molybdovanadophosphoric Acids and Their Salts. I. Investigation of Methods of Preparation and Characterization BY GEORGE A. TSIGDINOS AND
c. J.
HALLADA
Received Apvil 3, 1967 By the use of improved procedures, the free heteropoly acids Ha[PMol~VOaol. 3 4 H ~ 0 H , ~ [ P M O I O V Z.32HzO, O ~ O ] and Hs[ P M O ~ V ~.O ~ ~ ] were prepared reproducibly as orange crystalline solids. Potentiometric titration measurements showed 34H20 that the number of replaceable hydrogen ions in these free acids is four, five, and six, respectively. The salts Na4[PMon1 7 0 4 0 ] .8H20 and ( N H ~ ) ~ H [ P M O I ~.7.5H20 V O ~ ~ ] were prepared for the first time. The molybdovanadophosphate anion had unusually high hydrolytic stability. Infrared, visible, and ultraviolet spectra were obtained for these salts. Thermogravimetric and differential thermal analyses were performed on H~[PMoIIVO~O] 32HzO and N ~ ~ [ P M o I I V O ~ O ] 8Hz0. Potentiometric titration measurements with methanol as the solvent and NaOCHs as the titrant showed that the H~[PMOUVO acid ~ ~ is ] tetraprotic in solvents with low dielectric constants. 3
-
Introduction plished by physicochemical means discussed in this paper. The heteropolymolybdovanadates constitute an important class of heteropoly compounds on which only Experimental Section limited research has been conducted. The most well Prepurified grade sodium metavanadate containing 27' water known of these heteropolymolybdovanadates is the 10(Matheson Coleman and Bell) was used without further purifimolybdo-2-vanadophosphate(V) anion prepared by cation. All other reagents used were Baker Analyzed grade. K0korin.l I n 1964, Souchay and c o - w o r k e r ~ ~were -~ Preparation of Compounds. (a) 11-Molybdo-1-vanadophosable to replace molybdenum in the 12-molybdophosphoricAcid.--NazHP04, 7.1 g, was dissolved in 100 ml of water and mixed with 6.1 g of sodium metavanadate that had been phate anion structure by up to three pentavalent vanadissolved by boiling in 100 ml of water. The mixture was cooled dium atoms,2 but the compounds prepared were not and acidified to a red color with 5 ml of concentrated sulfuric acid. fully characterized and no analytical data were given.4 To this mixture was added a solution of 133 g of NaaMoO4.2HzO In work published in 1964, Krivy and Krti16assigned dissolved in 200 ml of water. Finally, 85 ml of concentrated a basicity of 3 to the l0-molybdo-2-vanadophosphoric sulfuric acid was added slowly with vigorous stirring of the solution. With this addition the dark red color changed to a lighter acid on the basis of radiometric titration studies emred. The heteropoly acid was then extracted with 400 ml of ploying cesium-137. They gave the salt the formula ethyl ether after the water solution was cooled. I n this exCS&L [P(Moz07)5VzOsI. traction, the heteropoly etherate was present as a middle layer; The present work elucidates the properties of the the bottom layer (water) was yellow and probably contained free acids and salts of the anions [ P M O ~ ~ V O ~ ~ ] *vanadyl -, species. After separation, a stream of air was passed through the heteropoly etherate layer to free it of ether. The [ P M O ~ ~ V Z Oand ~ ~ ][ ~P -M, O ~ V ~ O ~ OThe ] ~ - desired . free orange solid that remained was dissolved in 50 ml of water, conacids were obtained in a reproducible manner by using centrated to the first appearance of crystals in a vacuum desicdetailed, improved procedures. Further charactericator over concentrated sulfuric acid, and then allowed to crystalzation of the properties of these anions was accomlize further. The orange crystals that formed were filtered, (1) A . I. Kokorin, J. Geiz. Chem. C S S K , 24, 697 (1954). (2) M. P. Courtin, F. Chauveau, and P. Souchay, Compl. R e n d . , 268, 1246 (1964). (3) B. Charreton and G. Bertho, ibid., 261, 2903 (1965). (4) B. Charreton, F. Chauveau, G. Bertho, and P. Courtin, Chim. A n a l . (Paris), 47, 17 (1965). ( 5 ) I. Krivy and J. Kitil, Collecliolz Czech. Chern. C o m ? ~ u n .29, , 587 (1964).
washed with water, and air dried. The yield was 28 g. The crystalline acid effloresces slowly a t room temperature; thus the amount of water of crystallization varied slightly from sample to sample. Anal. Calcd for H ~ [ P M O I ~ V.32.5H20: O~~] P , 1.31; Mo,44.60; V, 2.15; H20,24.71. Found: P, 1.31; Mo, 44.54; V, 2.68; HzO (based on Mo), 24.86. The molar ratios are Mo to P, 10.97 to 1.00; and V to P, 1.24 to 1.00. Similar analyses were
Inorgunic Chemistry obtained in duplicate preparations of compounds reported in this paper. (b) IO-Molybdo-2-vanadophosphoric Acid.-Sodium metavanadate, 24.4 g , was dissolved by boiling in 100 ml of water and then mixed with 7.1 g of NaZHP04 in 100 ml of water. After the solution was cooled, 5 in1 of concentrated sulfuric acid was added, and the solution developed a red color. A n addition of 121 g of NazMoOc.2HZO dissolved in 200 ml of water was then made. While the solution was vigorously stirred, 85 ml of concentrated sulfuric acid was added slowly, and the hot solution was allowed to cool to room temperature. The 10-molybdo-2-vanadophosphoric acid was then extracted with 500 ml of ethyl ether. Air was passed through the heteropoly etherate (bottom layer) to free i t of ether. The solid remaining behind \vas dissolved in water, concentrated to first crystal formation, as already described, and then allowed t o crystallize further. The large red crystals that formed were filtered, washed with water, and air dried. The yield was 35 g. The solid effloresces slolrly a t room temperature. Anal. Calcd for Hs[PMo,oI'~O$'34.,5H20: P, 1.31; Mo, 40.69; V,4.32; H10, 26.33. Found: P, 1.34; Mo, 40.69; V,4.77; H20 (based o n M o ) , 26.32. Themolar ratios are: M o : P , 9.80:l.OO; V:P, 2.16:l.OO. Duplicate preparations gave similar analytical results. B s expected, this acid dissolved in ethyl ether to form an oil that is insoluble in ether. However, i t dissolves in other oxygencontaining solvents (ethyl alcohol, methanol, ethyl acetate, dimethyl sulfoxide, and tetrahydrofuran) to form single phases. 10-Molybdo-2-vanadophosphoric acid was also prepared by the method used by Kokorin,] the only modification being the substitution of Moos for the crystalline yellow MoOn. 2 H 2 0 . I n this preparation, 30.0 g of sodium metavanadate, 3.4 ml of 85% HaP04, and 74.0 g of molybdenum trioxide rvere refluxed in 800 nil of water for 8 hr. The acid was extracted with 200 ml of ether after acidification with 145 ml of concentrated hydrochloric acid and was subsequently recrystallized from water after the ether was removed. Anal. Calcd for H S [ P M O , ~ 1 7 ~ 0 ~ ~m 1 . 5 ~ ~ 0P, : 1.33; hio, 40.68; v, 4.32; H ~ O 26.33. , Found: P, 1.34; Mo, 41.34; V, 5.15; H2O (based on Mol, 25.14. The molar ratiosare: Mo:P,9.96:1.00; V : P , 2.33:l.OO. 7.1 g, (c) 9-Molybdo-3-vanadophosphoric Acid.-K'anHPOp, was dissolved in 50 ml of water and mixed with 36.6 g of sodium inetavanadate that had been dissolved by heating in 200 ml of water. After 5 ml of concentrated sulfuric acid n-as added to the cooled mixture, it attained a cherry red color. This solution was mixed with 54.5 g of NaaMo04.2H,0 dissolved in 150 ml of water, and then, while i t was being vigorously stirred, 85 ml of concentrated sulfuric acid was slowly added. The hot solution was allowed to cool to room temperature. The free acid was extracted with 400 ml of ethyl ethcr, the heteropolp etherate being the middle layer. The etherate was freed of ether when a stream of air was passed through the solution. The red solid remaining was dissolved in 40 ml of water and concentrated to crystal formation in a vacuum desiccator over concentrated sulfuric acid. The red crystals were filtered and washed with water. The yield was 7.2 g. The solid effloresces slovvly a t room temperature. A n d . Calcd for Ho[PMooVa04u].34H-520: P , 1.35; Mo, 38.76; 17, 6.71; HrO, 26.66. Found: P, 1.38; Mo, 38.78; V, 6.89; H20 (based on N o ) , 26.71. T h e molar ratios are: M o : P , 9.07: 1.00; V:P, 3.04: 1.00. A duplicate sample preparation gave similar analytical results. (d) Sodium 11-Molybdo- 1-vanadophosphate .-Twenty grams of H ~ [ P M O , , V O.35H20 ~ ~ ] was dissolved in 50 ml of water, and the resultant solution was slowly passed through a n ion-exchange column containing 20-50 mesh Dower 50-X8ion-exchange resin in the sodium form. The resin bed was 1.25 in. in diameter and 20 in. in height, The orange effluent containing the desired sodium salt was then placed in a vacuum desiccator over concentrated sulfuric acid for removal of water. Evaporation was continued t o dryness since this sodium salt is very soluble in water. Anal. Calcd for Nar[PMollVO40].8H20: Na, 4.57; P, 1.54; Mo, 52.42; V,2.53; H 2 0 , 7.15. Found: Na, 5.10; P, 1.51; Mo, 50.27; V, 3.08; HlO (based o n dehydration), 7.45.
(e) Preparation of Ammonium Salts.-Triaminoiiiuiii 11molybdo-1-vanadophospliatcand trianimonium lO-molybdo-2vanadophosphate were prepared b y the addition of solid ammonium chloride to solutions of the corresponding free acids. The orange solids that formed were filtered and washed with water, and then dried in a vacuurn desiccator over concentrated sulfuric acid. Anal. Calcd for (h'H4)3H[PM~ilV040] .3.5H20: N,2.21; P, 1.63; Mo, 55.68; V,2.69; H20,3.45. Found: N, 2.37; P, 1.66; Mo, 55.61; V, 2.88; H20 (based on Mo), 3.32. Anal. Calcd for ( X H ~ ) ~ H ~ [ P M O I O.7.5H20: T T ~ O ~ ~N, ] 2.18; P, 1.61; Mo, 49.88; T', 5.30; H?O,7.02. Found: ATT, 2.48; P, 1.65; Mo, 49.90; V,5.85; HnO (based 011 Mo), 6.99. Characterization of Compounds. (a) Analytical Procedures. -The molybdovanadophosphates were analyzed as described in the literature.6 T'anadium was separated from molybdenum and phosphorus by ion exchange after reduction to quadrivalent vanadyl cation followed by elution with dilute sulfuric acid and subsequent titrition with standard potassium permanganate. Molybdenum was determined gravimetrically by the a-benzoin oxime procedure; phosphorus mas determined by precipitation as magnesium ammonium phosphate and weighing as magnesium pyrophosphate. (b) Potentiometric Titrations.-All potentiometric titration measurements were performed with a Beckman Model H2 p H meter equipped with a standard calomel electrode and a glass electrode suitable for high-temperature measurements. The pH meter readings were repeated until a constant value was reached. ,411 solutions were magnetically stirred during the titration. The normality of the NaOH used was 0.1000 iV. The potentiometric titration of H ~ [ P M o : I V O in ~ ~methanol ] and in the m-ater-dioxane mixture was conducted using a saturated calomel electrode, a glass electrode, and a Precision vacuum tube voltmeter, PRV 63 (G. Bank Elektronik, Gottingen, West Germany). (c) Visible and Ultraviolet Spectra.-The absorption spectra of the acids H4[PMoliV040], H~[PMo10\~2040] , H~[PMOIV~O~O], and Ha[Ph'lol1040]in water were taken vith a Beckman DB automatic recording spectrophotometer employing 1-cm silica cells. (d) Infrared Spectra.-The infrared spectra of the three molybdovanadophosphoric acids and the 12-molybdophosphoric acid were obtained in hTujol mulls with a Perkin-Elmer 31 spectrophotometer. The infrared spectrum of 10-molybdo-2-vanadophosphoric acid was also obtained in a KBr disk and mas found t o be identical with that obtained in Xujol. (e) Differential Thermal Analysis (dta) and Thermogravimetric Analysis (tga).-A Harrop Precision Furnace Co. dta and tga unit was used for the dta and tga experiments.
Results and Discussion Preparation of the Compounds.-The free acids Hq[ P M O ~ ~ V O Hi ~ ~[PMoloVzOlo], ], and Ha[ P M O ~ V ~ O ~ ~ ] were prepared in very pure form according to the procedure described in the literature. However, the acidity specified for extraction into ether (5 N &Sod) was totally insufficient to accomplish extraction. Additional acid therefore had to be added. The analytical results could not be compared with those of Souchay and c o - ~ o r k e r s ~since - ~ they failed to publish such data. However, if the procedures outlined in this paper are strictly followed, products of very good purity can be obtained. The 10-molybdo-2-vanadophosphate and 9-molybdo3-vanadophosphate anions are not stable in the strongly acid media afforded by ion-exchange resins, reportedly the former being partially decomposed into the 11molybdo-1-vanadophosphatespecies and V02+ cations. The H6[PMo9V3040], which is difficult to prepare, is
'
(13) W. H. Priceand I
